The present invention relates to an exhaust manifold, and more particularly to an exhaust manifold for attachment by a motor flange to a cylinder head of an internal combustion engine with at least two in-line cylinders.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Exhausts from cylinders of a multi-cylinder internal combustion engines and carried away by an exhaust manifold are united in exhaust collectors. Exhaust manifolds can be made of cast steel or assembled from single steel sheets or pipe fittings welded to one another. Cast-steel manifolds can be produced in a fairly cost-effective manner even when their geometry is complex. Their weight however is normally higher than the weight of welded steel-sheet constructions. Also, cast-steel manifolds exhibit a greater thermal inertia than welded exhaust manifolds. On the other hand, welded exhaust manifolds with complex geometry are difficult to make and thus expensive. A benefit of welded exhaust manifolds is their low weight and their small heat capacity.
Also known are airgap-insulated exhaust manifolds having exhaust carrying ducts which are surrounded by a supporting outer shell at a distance to define an airgap. The outer shell is normally welded gastight with mounting flanges. Due to the complex construction, airgap-insulated exhaust manifolds are expensive.
In order to improve the efficiency of internal combustion engines, the engines are oftentimes charged by a compressor, typically a turbocharger. By making the turbocharger more efficient, it is possible to also increase the efficiency of the internal combustion engine. Charging of the internal combustion engine should occur quickly. This is possible only when the turbocharger quickly starts up so as to eliminate the undesired turbo lag. This requires however certain flow rates in order to prevent the gas impulse of combustion gases emitted from the motor from weakening in the exhaust manifold. Therefore, duct cross sections should be selected that they are not too big in cross section in order for the impulse to act substantially directly on the blades of the turbocharger or also to be able to realize its desired effect in a pressure-wave supercharger. Thus, when striving to provide a greatly contoured cross sectional geometry of the exhaust conducting ducts or exhaust manifold, the exhaust manifold becomes normally fairly complex. This poses a problem when manufacturing exhaust manifolds which have not been made by an original forming process because the sheet metal parts become more and more complex requiring complex configuration of the weld seam that further poses manufacturing problems so that the overall product quality and the product price are adversely affected.
It would therefore be desirable and advantageous to provide an improved exhaust manifold which obviates prior art shortcomings and which has little heat capacity and is easy to manufacture while resulting in a reliable and efficient operation of an internal combustion engine.